1. Field of the Invention
The present invention relates to a Session Initiation Protocol (SIP) based Voice over Internet Protocol (VoIP) system and a method of registering an SIP terminal therein.
2. Description of the Related Art
The SIP is a type of signal protocol designed for establishing/terminating sessions in an Internet Protocol (IP) network. It is well known as a VoIP telephone standard to locate and connect terminal users to a multi-group voice and video conference. Like the HyperText Transfer Protocol (HTTP), the SIP is versatile and convenient to use. The Internet Engineering Task Force (IETF) published RFC 2543 as the first version of the SIP in 1999, and more recently published RFC 3261 as the latest version of the SIP in June 2002.
While the SIP can adopt a User Datagram Protocol (UDP) or a Transmission Control Protocol (TCP) as a transfer means, it generally uses UDP in port 5060 as a reference value. When an SIP packet is lost owing to an unreliable protocol such as UDP, the SIP determines whether or not it has waited for a response for a sufficient time period, and then retransmits a command.
An SIP terminal generally uses a command “REGISTER” to be registered in a server. The SIP terminal transmits the “REGISTER” command to an SIP call server in order to register itself in the SIP call server.
Then, the SIP call server transmits a “401 Unauthorized” message to the SIP terminal. The “401 Unauthorized” message is a message requesting, for example, a user ID, password, nonce and domain of a “WWW-Authenticate” field.
A nonce is a parameter that varies with time. A nonce can be a time stamp, a visit counter on a Web page, or a special marker intended to limit or prevent the unauthorized replay or reproduction of a file. Because a nonce changes with time, it is easy to tell whether or not an attempt at replay or reproduction of a file is legitimate. That is, the current time can be compared with the nonce. If it does not exceed it or if no nonce exists, then the attempt is authorized. Otherwise, the attempt is not authorized.
Upon having received the “401 Unauthorized” message from the SIP call server, the SIP terminal transmits a user ID, password, nonce, domain and the like on a second “REGISTER” message to the SIP call server.
Then, the SIP call server performs an authentication in an MD5 mode to register the SIP terminal. That is, the SIP call server performs a registration through the user ID, password, nonce and domain of the SIP terminal from the “REGISTER” message transmitted from the SIP terminal as a method of registering the SIP terminal in a VoIP system based on the SIP (see RFC 3261).
Then, the SIP call server transmits a “200 OK” response message to the SIP terminal, completing the registration of the SIP terminal.
The use of a proxy server requires a register server. For example, when a telecommunication worker makes a connection to a VoIP telephone, the telephone sends a counterpart location to the register server. Several telephones can be registered by a single register server if there is an SIP gateway available in case of calling.
However, a conventional registration of a terminal in an SIP based VoIP system has drawbacks. That is, at self-initialization and thus re-registration of a previously registered terminal, if its authentication key is not identical, a new authentication key must be inconveniently generated again for re-registration.
Furthermore, when the IP of the terminal is changed, it is difficult to identify the terminal in case of a registration request and thus, registration errors can occur.